Can't believe what an algae eating machine my Kole Tang is!... He has only been in the upstairs tank now for 2 days, and almost totally cleaned the whole back glass (acrylic, actually) of all algae, leaving only the coralline. Here is a pic of part of it from before.
You can see how green it was (upper right). I had to regularly clean it with a scraper...
And this is today. You can see a bit of a pattern to his cleaning...
No wonder my downstairs tank (same sump and water as upstairs tank) was always so clean of algae... For sure now, am going to have to get another bristletooth tang for it, or it will likely soon get algae again.